This invention relates generally to the field of fixed-opening wrenches and more particularly to machining an open-ended wrench.
The open head at one or both ends of a handle of a standard fixed-jaw, open-ended wrench, is first forged then trimmed. The forging process leaves a web at the jaw end of the wrench and a rough finish of the interior surfaces of the jaws. The web is a thin layer of metal left in the area between the jaws of the wrench. The machining process presently used in the industry to remove the web and rough portions in the gripping area between the jaws of such wrenches is either broaching by the use of a broaching tool or milling by the use of a rotary cutter. Both broaching and milling leave either broaching or milling marks on the inner surface of the jaws opening. In addition, the jaws may spread during the broaching process and must be forced together after final heat treatment, with the result that some breakage could occur. A hardening, or heat treatment, process then follows. During the heat treatment some decarburization may occur because of minor variations in material chemistry with the result that the surface of the wrench is somewhat softened. Polishing or surface preparation, such as with nickel, chrome, or other materials completes the process.
Grinding of wrenches has generally not been used because of its impracticality; more particularly, grinding is a very slow operation and is very expensive. Also, the grinding wheel wears out with the result that the size of the grinding wheel changes so that all three sides of the jaw opening cannot be ground at the same time.
A grinding technique or process described in U.S. Pat. No. 3,984,213, issued Oct. 5, 1976 to W. Kelso, is generally known in the art as "creep feed grinding". Creep feed grinding involves slowly feeding the workpiece past a form grinding wheel set to the full depth of cut. The desired detail is produced in the workpiece in a single pass under the wheel. Also, parts are produced to a very high accuracy without burrs or distortion.
The Kelso patent is directed to the creep feed grinding of particular materials considered difficult to grind because of having a low machinability factor, namely AMS 5706 or the like, AMS 5663, AMS 5754, which has a machinability factor of 18, titanium, a titanium alloy, AMS 4928, and a cobalt base alloy, PWA 691. Although the patent mentions that the process is usable for materials presently ground in the conventional manner, it covers in fact materials normally considered difficult to grind by reason of wheel loading or thermal damage to the workpiece. The patent is limited to particular wheel surface speeds and feed rate of the workpiece relative to the workpiece.